1. Field of the Invention
The invention relates to a washer, more particularly to an improved leakproof washer.
2. Description of the Related Art
FIG. 1 illustrates a conventional washer (2) when incorporated on a screw fastener (1). The washer (2) is a resilient annular member with a predetermined thickness and serves to insure tightness and prevent leakage. In use, the washer (2) is sleeved on a threaded shank (11) of the screw fastener (1). When the screw fastener (1) is driven into a member (3), as shown in FIG. 2, the washer (2) is compressed such that the thickness thereof is reduced, while the diameter of the same is increased. The washer (2) is provided tightly between the member (3) and the head portion (12) of the screw fastener (1), thereby enabling the washer (2) to prevent water from leaking into the member (3) via the screw fastener (1). The washer (2) is indispensable in the construction industry especially when it is necessary to provide the screw fastener (1) with waterproofing capabilities. However, deformation and cracking of the washer (2) can occur after prolonged exposure of the latter to rain and sunshine, thereby preventing the washer (2) from accomplishing its purpose. Referring once more to FIG. 2, after the screw fastener (1) has been driven into the member (3) so as to force the washer (2) tightly against the latter, the washer (2) is unable to seal a clearance (D) formed between two adjacent screw threads (11) of the threaded shank (11). Therefore, when the washer (2) cracks and deforms, rain water can easily leak into the member (3) via the clearance (D). The washer (2) is thus unable to accomplish its purpose, thereby resulting in some construction problems.
Since the conventional washer (2) is unable to provide adequate protection against leakage, it has been known to provide a hardening agent (such as silicone) to enclose the head portion (12) of the screw fastener (1). The hardening agent cures upon contact with air and prevents leakage of water into the member (3). However, application of the hardening agent requires additional manpower, thereby increasing the labor costs incurred and prolonging the construction period.